This age bracket, bigger than any other, is pushing companies to revamp marketing and products, including a lot of remedial education

The Scotts Miracle-Gro Co. has started offering gardening lessons for young homeowners that cover basic tips—really, really basic—like making sure sunlight can reach plants.

“These are simple things we wouldn’t have really thought to do or needed to do 15 to 20 years ago,” says Jim King, senior vice president of corporate affairs for Scotts. “But this is a group who may not have grown up putting their hands in the dirt growing their vegetable garden in mom and dad’s backyard.”